diff --git a/docs/notebooks/boundaries.ipynb b/docs/notebooks/boundaries.ipynb
index d860c18..0e5fb38 100644
--- a/docs/notebooks/boundaries.ipynb
+++ b/docs/notebooks/boundaries.ipynb
@@ -107,8 +107,10 @@
     "\n",
     "\n",
     "def eq(k, kp):\n",
-    "    z = 2 / 3 * (2 - (kp + k) / nside)\n",
-    "    phi = np.pi / 4 / nside * (nside - kp + k)\n",
+    "    z = 2/3 * (2 - (abs(kp) + abs(k)) / nside)\n",
+    "    phi = np.pi/4/nside * (nside - abs(kp) + abs(k))\n",
+    "    phi = np.where(k >= 0, phi, -phi)\n",
+    "    phi = np.where(kp >= 0, phi, np.pi - phi)\n",
     "    return phi, z\n",
     "\n",
     "\n",